Hollow-cathode discharge tube for generating atomic resonance lines



Feb. 1966 HIROSHI OKAGAKl ETAL 3,233,136

HOLLOW-CATHODE DISCHARGE TUBE FOR GENERATING ATOMIC RESONANCE LINES Filed April 5, 1962 United States Patent 3,233,136 HGLLOW-CATHGDE DISCHARGE TUBE FOR GENERATHNG ATOMIC RESQNANCE LINES Hiroshi Okagaki and Yasushi Ikuta, Tokyo-to, Japan, assignors to Kabushiki Kaisha Hitachi Seisnkusho,

Tokyo-to, Japan, a joint-stock company of Japan Filed Apr. 3, 1962, Ser. No. 184,778 Claims priority, application Japan, Apr. 8, 1961, 36/ 17,519 2 Claims. (Cl. 315-110) This invention relates to a new hollow-cathode discharge tube for generating atomic resonance lines, of simple construction wherein the rate of blackening of the extraction window for extracting atomic resonance lines is reduced considerably by the provision of a novel extraction window.

It is known that, in an atomic absorption spectrophotometer, the cathode sputtering in the glow discharge region in a hollow-cathode discharge tube is utilized to cause the generation of atomic resonance lines, and these are projected onto a flame sample to cause emergence of the required absorption lines. In a conventional hollowcathode discharge tube, however, the sputtering of the cathode accompanying glow discharge causes not only blackening of the glass tube at the surrounding parts but also blackening of the extraction window for the atomic resonance lines. Consequently, its transmission function is impaired, and the strength of the atomic resonance lines is lowered.

It is an object of the present invention to remove the above-stated disadvantage of conventional hollow-cathode discharge tubes.

More specifically, it is an object of the invention to provide a new hollow-cathode discharge tube wherein the rate of blackening of the extraction window is considerably low.

It is another object of the invention to provide a hollow-cathode discharge tube as stated above which has simple construction.

The nature of the invention, its details, and the manner in which its objects may best be achieved will be apparent by reference to the following description when taken in conjunction with the accompanying drawing which is a side view, in longitudinal section, indicating the construction of one embodiment of the invention.

Referring to the drawing, the discharge tube according to the invention comprises a tube 1 made of such a substance as glass, a discharge anode 2 positioned within the tube 1 at the terminal end, near the tube wall, a hollow cathode 3 disposed coaxially within the tube at the terminal end, leadout wires 4 and 5 connected respectively to the discharge anode 2 and the hollow cathode 3, an extraction window 6 for atomic resonance lines, which is a principal feature of the invention, a hollow cylinder 7 which is made of such a material as a glass tube, and which is so positioned coaxially in the tube 1 as to extend into the tube 1 to a suitable axial length, and a transmittive wall 8 made of such a material as quartz or glass which is secured to the outer end of the cylinder 7.

In the hollow-cathode discharge tube according to the present invention as described above, an atomic resonance line corresponding to the cathode material is generated by the cathode sputtering accompanying the glow discharge between the anode 2 and the cathode 3, and this is emitted through the transmittive wall 8. The foregoing function is the same as that in the case of a conventional hollow-cathode discharge tube. In the case of the present invention, however, of the fine metallic particles created by the afore-mentioned cathode sputtering, particularly those which intersect the axial direction of the cylinder 7 at the extraction window 6 and fly off, that is, those which fly olf obliquely from the very beginning of sputtering, as well as such particles as those whose paths are bent during their motion within the tube by such causes as collision with the filler gas within the tube, convection current, or diffusion, all adhere to the outer Wall or inner wall of the cylinder 7. Accordingly, most of these particles do not reach the transmittive wall 8, and only a few particles which travel within the cylinder 7 parallel to its axis reach the wall 8 and adhere to its inner surface. Therefore, as compared to the case of the conventional hollow-cathode discharge tube, wherein a window is fitted directly into the tube wall, and not only the fine particles of metal which are projected directly, but all such particles as those which reach the window surface from oblique directions, adhere to the window surface, the degree of blackening in the tube according to the present invention is extremely low. Accordingly, the hollow-cathode discharge tube according to the invention is capable of accomplishing emission of atomic resonance lines with high efliciency over a long period of time. Moreover, since this discharge tube has an extremely simple construction, it can be utilized with great effectiveness in such apparatuses as atomic absorption spectrophotometers.

Although this invention has been described with respect to a particular embodiment thereof, it is not to be so limited as changes and modifications may be made therein which are within the full intended scope of the invention, as defined by the appended claims.

What is claimed is:

1. A hollow-cathode discharge tube for generating atomic resonance lines which consists of a glass tube as outer casing; a discharge anode disposed at one end of said tube near its wall; a hollow cathode disposed in said tube coaxially and concentrically therewith and at the same end as said anode; lead out wires fastened to said anode and said cathode and penetrating the end of said tube; a hollow glass cylinder disposed in said tube, coaxially and concentrically therewith at its opposite end, its far end protruding through and beyond said tube; an extraction window for atomic resonance lines closing the inner end of said cylinder; and a transmittive wall closing its outer end.

2. A hollow-cathode discharge tube for generating atomic resonance lines which consists of a straight cylindrical glass tube, closed at both ends, as an outer casing; a discharge anode disposed at one end of said tube, near and parallel to, its wall; a hollow cathode disposed in said tube coaxially and concentrically therewith and at the same end as said anode; lead out wires fastened to said anode and said cathode and penetrating the end of said tube; a hollow glass cylinder disposed in said tube, coaxially and concentrically therewith, at its opposite end, its far end protruding through and beyond the end of said tube; an extraction window for atomic resonance lines closing the inner end of said hollow glass cylinder; and a transmittive wall closing its outer end; said wall being of a material selected from the group consisting of glass and quartz.

References Cited by the Examiner UNITED STATES PATENTS DAVID J. GALVIN, Primary Examiner. 

1. A HOLLOW-CATHODE DISCHARGE TUBE FOR GENERATING ATOMIC RESONANCE LINES WHICH CONSISTS OF A GLASS TUBE AS OUTER CASING; A DISCHARGE ANODE DISPOSED AT ONE END OF SAID TUBE NEAR ITS WALL; A HOLLOW CATHODE DISPOSED IN SAID TUBE COAXIALLY AND CONCENTRICALLY THEREWITH AND AT THE SAME END AS SAID ANODE; LEAD OUT WIRES FASTENED TO SAID ANODE AND SAID CATHODE AND PENETRATING THE END OF SAID TUBE; A HOLLOW GLASS CYLINDER DISPOSED IN SAID TUBE, COAXIALLY AND CONCENTRICALLY THEREWITH AT ITS OPPOSITE END, ITS FAR END PROTRUDING THROUGH AND BEYOND SAID TUBE; AN EXTRACTION WINDOW FOR ATOMIC RESONANCE LINES CLOSING THE INNER END OF SAID CYLINDER; AND A TRANSMITTIVE WALL CLOSING ITS OUTER END. 